This invention relates to a new type of construction for the liquid processing vessel in a sandmill. More specifically, the invention relates to an improved arrangement for dispersing the liquid introduced into the sandmill and to an improved arrangement for mounting filter screen at the output end of a sandmill vessel.
Sandmilling is a proven, practical, continuous, high production method of dispersing and milling particles in liquids to produce smooth, uniform, finely dispersed products. One good example of this is the dispersement of pigment agglomerates in paints. The process is also applicable to a wide variety of inks, dye stuffs, paper coatings, chemicals, magnetic tape coatings, insecticides and other materials where milling to a high degree of fineness is required.
In a typical sandmilling process, the material or slurry to be processed is introduced at the bottom of a processing chamber and pumped upwardly through grinding media, which is often referred to as sand, although it is normally a small diameter manufactured grit rather than sand. Rotors positioned within the vessel forming the processing chamber grind the slurry as it is pumped through the media.
Usually the sandmill vessel is cylindrically shaped and is mounted on a support column with the rotor axis extending vertically parallel to the column. The motor to drive the rotor is normally mounted in the upper portion of the support column and belts are utilized to transmit the rotational force of the motor to a pulley attached to the upper end of the drive shaft that extends downwardly into the vessel where it is attached to the rotor.
One problem associated with the typical sandmill is that the liquid or slurry introduced to the bottom of the vessel, being of a relatively thick consistency, tends to concentrate at the point of introduction and therefore often fails to disperse evenly around the rotors.
Typically the processed slurry or liquid exits the vessel at its upper terminus. Since the liquid may contain suspended particles of the grinding media, it is found to be advantageous to incorporate a filtering screen at the vessel's outlet. Typically, such a filtering screen is an annular member attached to the upper portion of the vessel. A typical arrangement for the filtering screen is disclosed in U.S. Pat. No. 3,135,474 to Schold. One problem with such an arrangement results from the necessity for frequently removing the screen for cleaning and maintenance. With an arrangement such as that disclosed in the Schold patent it is necessary to remove the entire vessel from its support structure, a process which is both time consuming and inconvenient.
Hence, a need has been felt for providing a sandmill vessel which incorporates a means for dispersing the slurry or liquid to be processed at the inlet end and which also provides a filter screen that is quickly and easily detached from the unit without the necessity for removing the entire vessel.